1. Field of the Invention
This invention generally relates to integrated circuits (ICs) and, more particularly, to fluidic assembly method for the fabrication of emissive displays.
2. Description of the Related Art
The fluidic transfer of microfabricated electronic devices, optoelectronic devices, and sub-systems from a donor substrate/wafer to a large area and/or unconventional substrate provides a new opportunity to extend the application range of electronic and optoelectronic devices. For example, display pixel size light emitting diode (LED) micro structures, such as rods, fins, or disks, can be first fabricated on small size wafers and then be transferred to large panel glass substrate to make a direct emitting display. One conventional means of transferring these LED microstructures is through a pick-and-place process. However, with a display comprising millions of elements, such a process may take several hours to complete and is therefore inefficient.
The fluidic self-assembly of electronic devices, such as LEDs and concentrated photovoltaics, is often performed by surface energy minimization at molten solder capillary interfaces so that both mechanical and electrical connections can be made to an electrode during assembly, as demonstrated in U.S. Pat. No. 7,774,929. In one aspect, electronic devices are captured in shape-matched well structures, followed by electrical integration processes, as demonstrated in U.S. Pat. No. 6,316,278.
Some problems yet to be addressed with conventional fluidic assembly processes are related to the distribution method over large scales, the integration of microcomponents to drive circuitry over large areas, and the potential mechanisms for the repair of defective microcomponents. Over large scales, conventional fluidic assembly into wells is challenged by the dual requirements of maximum velocities for microcomponent capture and minimum distribution velocities for high-speed array assembly. Similarly, achieving the microcomponent dispense scheme and flow velocity uniformity necessary for a high yield over the whole assembly substrate becomes very challenging over greater-than-centimeter scales.
The integration of assembled microcomponents has been primarily done via photolithographically defined electrode deposition for microcomponents, or else by lamination of the second electrical contact in approaches where the first electrode contact is made as part of the assembly scheme. However, the photolithography of large substrates after fluidic assembly is potentially prohibitive due to the contaminating nature of any residual microcomponents on the substrate surface. Laminated top contacts have not demonstrated sufficiently reliable electrical connection to microcomponents for display applications.
Lastly, defect detection of electrically excited microcomponents is the most reliable and robust approach for inspection preceding repair. Assembled microcomponents with top-contact electrodes are at least partially held in an insulating matrix. Any repair that involves removal of defective microcomponents from this matrix is extremely difficult. Moreover, any similarly integrated microcomponents that are added to the array to compensate for defective microcomponents requires that the electrode contact process to be repeated. While technical workarounds may exist, they are expected to be more expensive, more time-intensive, and less reliable.
It would be advantageous if a fluidic assembly process could be used to efficiently transfer emissive elements to a display substrate with a minimum of process steps.